fix(ui-slash): make the reference lexicon reactive end to end

The decoration scan read a mutable lexicon() aggregation during render
with no subscription, so a catalog settling or a child spawning after
prewarm left drafted tokens undecorated until an unrelated re-render.
The controller now publishes the aggregation as a snapshot store fed by
a new optional SlashSource.subscribeLexicon hook (ui-skill notifies on
settle/invalidate, ui-subagent forwards the session-list feed), the
composer keyboard face exposes it as an observable, and InputBar
subscribes through uSES. Sources registered after scope birth now warm
and join live controllers via a service broadcast.

packages/client/ui-conversation/src/client/input/contract.ts

@@ -5,7 +5,7 @@
  * conversation wiring layer alone sees the full SessionInput. InputMachine
  * (machine.ts) is package-private and never exported.
  */
-import type { ClientContext, SnapshotStore } from '@deepseek-ai/dsh-client-runtime/client'
+import type { ClientContext, ObservableSnapshot, SnapshotStore } from '@deepseek-ai/dsh-client-runtime/client'
 import type {
   ArbitrateKey, ArbitrateOutcome, CommandClaim, ConsumeTokenRequest, PickOutcome,
   ReferenceInsert, SubmitOutcome, TokenSpan,
@@ -99,8 +99,8 @@ export interface ComposerKeyboard {
   space(): boolean
   /** Dismiss the popupSelect shell (any interaction outside the box). */
   dismissPopup(): void
-  /** Hot plain-text reference lexicons for the decoration scan (decision 21; empty Map without a pipeline). */
-  lexicon(): ReadonlyMap<'/' | '@', readonly string[]>
+  /** Hot plain-text reference lexicon source for the decoration scan (decision 21; empty Map without a pipeline). */
+  readonly lexicon: ObservableSnapshot<ReadonlyMap<'/' | '@', readonly string[]>>
 }
 
 /** One queued-message row projected from the session/queued frames (T9 supplies the store). */

packages/client/ui-conversation/src/client/input/facade.ts

@@ -206,11 +206,14 @@ export class SessionInputShell implements SessionInput {
   }
 
   /**
-   * Hot plain-text reference lexicons for the decoration scan (decision 21).
-   * @returns the controller's per-trigger aggregation; empty Map without a pipeline.
+   * Hot plain-text reference lexicon source for the decoration scan
+   * (decision 21): delegates to the controller's aggregated store. Stable
+   * identity per shell; without a pipeline the snapshot is the empty Map and
+   * subscribers never fire.
    */
-  lexicon(): ReadonlyMap<'/' | '@', readonly string[]> {
-    return this.deps.slash?.()?.lexicon() ?? EMPTY_LEXICON
+  readonly lexicon: ObservableSnapshot<ReadonlyMap<'/' | '@', readonly string[]>> = {
+    getSnapshot: () => this.deps.slash?.()?.lexicon.getSnapshot() ?? EMPTY_LEXICON,
+    subscribe: fn => this.deps.slash?.()?.lexicon.subscribe(fn) ?? (() => {}),
   }
 
   /**

packages/client/ui-conversation/src/client/skeleton/InputBar.tsx

@@ -36,6 +36,11 @@ export function InputBar({
     (fn: () => void) => noticeStore.subscribe(fn),
     () => noticeStore.getSnapshot(),
   )
+  const lexiconStore = keyboard.lexicon
+  const lexicon = useSyncExternalStore(
+    (fn: () => void) => lexiconStore.subscribe(fn),
+    () => lexiconStore.getSnapshot(),
+  )
   const promptError = useSession(s => s.promptError)
   const running = useSession(s => s.running)
   const disabled = useSession(s => s.removed)
@@ -244,7 +249,7 @@ export function InputBar({
   // claim token highlights through behind the textarea glyphs; each U+FFFC
   // placeholder renders as a chip (the textarea's own glyph is invisible, the
   // backdrop chip supplies the visual); the claim hint is ghost text.
-  const deco = deriveDecorations(input, keyboard.lexicon())
+  const deco = deriveDecorations(input, lexicon)
   const backdrop: ReactNode[] = []
   {
     // Segment boundaries: the token range end, every chip offset, and every